Methods for passivating metal powder condensate from additive manufacturing processes

ABSTRACT

A method for passivating metal-containing powder condensate and the resulting passivated metal. A metal-containing powder condensate comprising at least one metal is combined with at least one binder and at least one solvent to form a slurry, wherein the solvent only partially dissolves the powder-binder mixture. The resulting slurry is dried to remove excess solvent, forming a passivated metal-binder solid cake.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 63/341,685, filed on May 13, 2022, which is incorporated byreference herein.

TECHNICAL FIELD

The present invention relates to methods for passivatingmetal-containing powder condensate from powder bed fusion additivemanufacturing processes.

BACKGROUND

During additive manufacturing (AM) processes also known as 3D printingor powder bed fusion (PBF), potentially hazardous waste streams areproduced. The waste streams contain solidified particles within a vaporplume resulting from evaporation of a metal or metal alloy beingdeposited into a build chamber within the additive manufacturingprinter. These solidified particles are sometimes called powdercondensate and often have hazardous properties or high risks ofcombustion and require appropriate disposal. Depending on the differentfiltering systems on the printing machines, the powder condensate mayalso contain chalk, silica sand, or other non-metallic powders that arepart of the current state of the art process to inert the powdercondensate.

Powder condensates also contain one or more metals and/or metal alloysthat could be economically recovered for future additive manufacturingprocesses or metal production. However, due to the hazardous nature ofthe powder condensate, transportation and reclamation of metal and/ormetal alloys from the powder condensate can require multipletime-consuming and costly processes to satisfy hazardous material safetyconcerns as well as produce a functional feed powder for other additivemanufacturing processes or metal production.

To safely handle the metals and/or metal alloys following the additivemanufacturing process, powder condensate has been passivated in the pastby mixing the powder condensate with material such as silica sand, glassbeads, other non-metallic powders and/or inert liquids such as mineraloil. This process passivates the condensate and makes the transportationpossible without risk of ignition, but the metal powder must betransported and disposed of as hazardous. Traditional passivationprocesses also do not always allow for economic recovery of themetal/metal alloy.

There is still a need, therefore, for a passivation treatment processthat mitigates hazardous material storage and transport logistics andalso allows for the efficient and effective recovery of metals/metalalloys from the condensate for future use.

SUMMARY

Methods for passivating metal-containing powder condensate andpassivated metal-containing powder condensates are provided herein. Inone method for passivation, a metal-containing powder condensate and atleast one binder can be combined to form a powder-binder mixture,wherein the metal-containing powder condensate comprises at least onemetal. The powder-binder mixture can then be combined with at least onesolvent to form a slurry, wherein the solvent only partially dissolvesthe powder-binder mixture. The resulting slurry is then dried to form apassivated metal-binder solid. This drying step removes excess solventfrom the slurry, forming a passivated metal cake. The passivated metalcake being a plurality of metal particles each substantially coated inbinder.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying Figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 depicts a flow chart of an illustrative process for making anon-reactive metal powder cake, according to one or more embodimentsdescribed herein.

FIG. 2 depicts a photograph of two non-reactive metal powder cakes.

DETAILED DESCRIPTION

It is to be understood that the following disclosure describes severalexemplary embodiments for implementing different features, structures,and/or functions of the invention. Exemplary embodiments of components,arrangements, and configurations are described below to simplify thepresent disclosure; however, these exemplary embodiments are providedmerely as examples and are not intended to limit the scope of theinvention. Additionally, the present disclosure can repeat referencenumerals and/or letters in the various exemplary embodiments and acrossthe Figures provided herein. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various exemplary embodiments and/or configurationsdiscussed in the Figures. Moreover, the exemplary embodiments presentedbelow can be combined in any combination of ways, i.e., any element fromone exemplary embodiment can be used in any other exemplary embodiment,without departing from the scope of the disclosure.

Described herein are methods for passivating metal-containing powdercondensate from additive manufacturing processes and the resultingpassivated metal-containing powder cakes. In certain embodiments,metal-containing powder condensate is mixed with one or more solidbinder agents to provide a physical blend of the agent and themetal-containing condensate. This physical blend can then be at leastpartially solubilized in one or more solvents to provide a slurry orsolution. In an alternative embodiment, the metal-containing powdercondensate can be mixed in one or more solvents to provide a mixture ofthe solvent and condensate. One or more solid binder agents can then beadded to this mixture to at least partially solubilize the binder agentto form a slurry or solution. In yet another alternative embodiment, theone or more solvents can be mixed with the one or more binder agents tocreate an at least partially solubilized mixture of these components,and the metal-containing powder condensate can be added to the mixture.The solvent can then be removed from the formed solution or slurry, byevaporation, for example, leaving behind a cake of the metal-containingpowder particles substantially coated by the binder.

All numerical values within the detailed description and the claimsherein are modified by “about” or “approximately” the indicated value,and take into account experimental error and variations that would beexpected by a person having ordinary skill in the art.

Certain terms are used throughout the following description and claimsto refer to particular components. As one skilled in the art willappreciate, various entities may refer to the same component bydifferent names, and as such, the naming convention for the elementsdescribed herein is not intended to limit the scope of the invention,unless otherwise specifically defined herein. Further, the namingconvention used herein is not intended to distinguish between componentsthat differ in name but not function.

The term “or” is intended to encompass both exclusive and inclusivecases, i.e., “A or B” is intended to be synonymous with “at least one ofA and B,” unless otherwise expressly specified herein.

The terms “binder” and “binding agent” are used interchangeably, andboth refer to any material that can adhere to another material and/orcoat another material. Any suitable binder can be added to the powdercondensation. Suitable binders can include, for example, polyvinylbutyral (PVB), polylactic acid (PLA), polyurethanes, ethylene vinylacetate (EVA), polycarbonates, polypropylene (PP), propylene elastomers,ethylene propylene rubber (EPR), ethylene propylene copolymers (EPC),polyisobutylene (PIB), styrene butadiene rubber (SBR), polyolefins,polyethylene-co-poly-1-octene (PE-co-PO), PE-co-poly(methylenecyclopentane) (PE-co-PMCP), acrylics, poly methyl-methacrylate,polyvinylacetacetal resin, polyvinyl acetal resin, stereoblockpolypropylenes, polymethylpentene copolymer, polyethylene oxide (PEO),PEO block copolymers, molasses, and the like.

The term “solvent” refers to any liquid at room temperature that can atleast partially dissolve or solvate the binder and powder condensateblend. Any suitable solvent can be used. Suitable solvents, include, butare not limited to, for example, water, silicone, molasses, organic andinorganic acids, any one or more aliphatic hydrocarbons, such asisobutane, butane, pentane, isopentane, hexanes, isohexane, heptane,octane, dodecane, and mixtures thereof; cyclic and alicyclichydrocarbons, such as cyclohexane, cycloheptane, methylcyclohexane,methylcycloheptane, and mixtures thereof. In an embodiment, the solventis not aromatic, or aromatics are present in the solvent at less than 1wt %, or less than 0.5 wt %, or less than 0.05 wt %, based upon theweight of the solvents. More specific solvents can include ethanol,isopropyl alcohol (IPA), isopentane, hexane.

As used herein the phrase “removing a solvent,” refers to the processwhereby a solvent is removed or separated from the components ormaterials set forth herein. The solvent can be removed using anyconventional separation technique, including crystallization,evaporation, filtration, membrane separation, distillation, vacuum orother reduced pressure separation techniques. The conditions toeffectuate an efficient separation of the solvent could be readilydetermined by those of ordinary skill in the art of chemicalseparations.

As used herein, the term “metal-containing” refers to a material that isor contains at least one metal or a mixture of a metal and at least oneother chemical element. A “metal-containing powder condensate” refers toany by-product of an additive manufacturing processes that uses one ormore metals or metal alloys. The metals can be selected from any of themetals of Group 3 to Group 12 of the Periodic Table of Elements and/orother metals from Groups 13-15. For example, the metals can be, but notlimited to, iron, nickel, titanium, tungsten, cobalt, copper, chrome,gold, silver, platinum, rhodium, mercury or any combinations thereof.Other metals can be aluminium, tin, or lead. Illustrative alloys can beor can include any two or more metals described herein. Otherillustrative alloys can be or can include steel, stainless steel,silicon steel, solder, brass, pewter, duralumin, red gold, white gold,sterling silver, bronze, and amalgams. In a preferred embodiment, themetal-containing powder condensate is a metal alloy with a nickel base.

A more detailed description of the methods for passivatingmetal-containing powder condensate from additive manufacturing processeswill now be described with reference to the figures provided. FIG. 1depicts an illustrative flow chart of a process for making anon-reactive metal powder cake. A metal-containing powder condensate canbe collected from an additive manufacturing process or any other sourceof metal-containing powder condensate. For example, the metal-containingpowder condensate can be collected from an additive manufacturingprocess whereby the condensate is generated when a laser in a 3Dprinter, for example, vaporizes a small percentage of the metal/metalallow powder being used to make a part in the build area of the printer.This vapor is flushed from the build area via a gas flow and condensedon a filter that cleans the flowing gas. The condensed powder falls fromthe filter and is then collected in solid form in a collection bin. Thismetal-containing powder condensate can then be combined with one or morebinders or binding agents to provide a physical mixture or blendthereof. This blend can then be mixed with one or more solvents to atleast partially dissolve the binder/metal blend to form a solution orslurry. The resulting solution or slurry can be homogeneous or not. Insome embodiments, the blend can be completely dissolved into ahomogenous or non-homogenous solution or only partially dissolved into aslurry or paste that can be homogenous or non-homogenous. The solvent ispreferably mixed into the blend of the metal-containing powdercondensate and binder to provide a homogenous mixture.

Alternatively, the solvent can first be added to the metal-containingpowder condensate and then the binder can be added to the mixture of thesolvent and metal-containing powder condensate. In another alternativeembodiment, the one or more solvents can be mixed with the one or morebinder agents first to create an at least partially solubilized mixtureof these components, and then the metal-containing powder condensate canbe added to the solution or slurry of the one or more solvents andbinder(s).

After the formation of the slurry or solution, a desirable amount of thesolvent can be removed. For example, the solvent can be subjected tothermal energy and evaporated, resulting in a passivated metal cake. Thepassivated metal cake being a plurality of metal or metal alloyparticles each substantially coated in the binder. In one or moreembodiments, the removed solvent can be condensed and recycled to treatanother blend batch. Preferred solvents can be evaporated at atmosphericpressure at temperatures less than 300° C., 250° C., 200° C., or 150° C.

The coated metal-containing powder particles within the cake arepassivated using the binder coating and thus, are non-reactive such thatthe metal cake does not explode, combust, corrode, or otherwise reactwith its surrounding environment. The non-hazardous and non-explosive,passivated metal cakes can be stored, transported, and recycled, withoutregulatory restrictions. Upon receipt of the passivated powder, thebinder can be separated from the metal through the appropriate use ofheat, chemical treatments, and the like. The metal will then be suitableas raw material to produce new metal products or powders.

Each non-reactive metal-containing powder cake can have a mass ratio ofmetal powder to binder. The mass ratio of metal-containing powdercondensate to binder preferably ranges from a low of 1 kg/22 g, 1 kg/20g, or 1 kg/18 g, to a high of 1 kg/12 g, 1 kg/10 g, or 1 kg/8 g. Thebinder/metal-containing powder condensate blend can contain at least 50wt %, 60 wt %, 70 wt %, 80 wt %, 90 wt %, 95 wt % or 99 wt % of themetal condensate, based on the total weight of the blend; the balancebeing the one or more binders.

When the one or more solvents are added to the binder/metal-containingpowder condensate blend, the resulting mixture can contain at least 5 wt%, 10 wt %, 15 wt %, 20 wt %, 35 wt %, 55 wt %, 65 wt %, 80 wt %, 85 wt%, 90 wt %, or 95 wt % of the blend, the balance being solvent. Theamount of the metal-containing powder condensate in the resultingmixture can range from a low of about 15 wt %, 25 wt % or 30 wt % to ahigh of about 50 wt %, 70 wt %, or 90 wt %.

While compositions and methods are described herein in terms of“comprising” various components or steps, the compositions and methodscan also “consist essentially of” or “consist of” the various componentsand steps. As used herein “consisting essentially of” means that thedescribed/claimed composition does not include any other components thatwill materially alter its properties by any more than 5% of thatproperty, and in any case, does not include any other component to alevel greater than 3 wt %.

As used herein, “substantially no,” and “substantially free of” areintended to mean that the subject item is not intentionally used oradded in any amount but can be present in very small amounts existing asimpurities resulting from environmental or process conditions.

To provide a better understanding of the embodiments of the presentinvention, the following non-limiting examples of preferred orrepresentative embodiments are given. In no way should the followingexamples be read to limit, or to define, the scope of the invention.

EXAMPLES

Three examples were prepared as summarized in Table 1 below. Examples 1and 2 were Haynes 282 metal alloy powder condensates and were filteredusing a filtering system that does not contain chalk. Example 3 was anInconel 718 metal alloy powder condensate and was filtered using afiltering system that contained chalk.

Examples 1 and 2 were mixed with a PVB binder using a plastic spoonwhile adding IPA solvent to form a paste of desired consistency suchthat the fluidity of the mixture allowed for the metal powder to befully coated in liquidus resin. The slurries were left to dry at ambienttemperature (about 23° C.) on an aluminum tray with parchment paper toprevent sticking to the tray.

TABLE 1 Blend compositions of Examples 1-3 Powder Binder Solvent (grams)(grams) (mL) Example 1 250 5 40 Example 2 1,000 15 150 Example 3 237 540

The three slurries formed a dense paste that air dried after a fewhours. Examples 1-2 were not a continuous solid and with little pressurebecame crumbs. Example 3 was a complete and continuous solid.

FIG. 2 depicts a photograph of two non-reactive metal powder cakes. Thecake on the left 210 had a mass ratio of 1 kg of Inconel 718 metal to 20g PVB binder. The cake on the right 220 had a mass ratio of 1 kg ofHaynes 282 metal alloy to 10 g PVB binder. As depicted, both powdercakes looked like burned hamburger patties with similar consistency.Both were continuous solids and had little to no crumbs.

During the trials no hazardous situations were reported, and the airquality remained within acceptable limits.

Preliminary results from these trials determined that Example 3, thatwas 237 g of metal-containing powder condensate mixed with 5 g of PVBand 40 mL of IPA, formed a solid, passivated cake that can be safelytransported. While Examples 1 and 2 were also successful in creating asolid passivated cake, they resulted in a non-optimal, brittle solid.

Various terms have been defined above. To the extent a term used in aclaim is not defined above, it should be given the broadest definitionpersons in the pertinent art have given that term as reflected in atleast one printed publication or issued patent. All numerical values inthis disclosure may be exact or approximate values unless otherwisespecifically stated. Accordingly, various embodiments of the disclosuremay deviate from the numbers, values, and ranges disclosed hereinwithout departing from the intended scope.

Furthermore, all patents, test procedures, and other documents cited inthis application can be fully incorporated by reference to the extentsuch disclosure is not inconsistent with this application and for alljurisdictions in which such incorporation is permitted.

While the foregoing is directed to more preferred embodiments of thepresent invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A method for passivating metal-containing powdercondensate, comprising: combining a metal-containing powder condensateand at least one binder to form a powder-binder mixture, wherein themetal-containing powder condensate comprises at least one metal;combining the powder-binder mixture with at least one solvent to form aslurry, wherein the solvent only partially dissolves the powder-bindermixture; and drying the slurry to form a passivated metal-binder solid,wherein drying removes excess solvent from the slurry.
 2. The method ofclaim 1, wherein the at least one metal is nickel.
 3. The method ofclaim 1, wherein the binder is polyvinyl butyral.
 4. The method of claim1, wherein the solvent is isopropyl alcohol.
 5. The method of claim 1,wherein the drying is performed by evaporation.